There are known hard disk storage units, or “hard disks”, for storing and recalling data, that are employed in electronic systems such as computers. Hard disks typically include one or more magnetic read/write heads that are connected to sliders and are placed near a surface of a rotating magnetic disk. When the magnetic disk is driven into rotation, a thin air cushion forms between the disk and the slider, enabling the latter to “float” over the disk at a distance which is in the range of a few tens of nanometers, or even less, in the current hard disks. In the course of the disk rotation, the magnetic read/write elements can be utilized to read/write bits of data along a magnetic track on the magnetic disk.
It is known that the heads employed in the known hard disks are very complex and delicate and thus are checked before the assembly in the hard disks.
Generally, the heads are checked once they have been assembled in “Head Gimbal Assembly” (HGA) or one or more HGA have been assembled in a “Head Stack Assembly” (HSA). Typically, the HGA includes a head with an associated slider, and a resilient thin plate to which the head is connected by means of a joint. Each of the thin plates has one end, opposite with respect to the end carrying the head, which is connected to a E-shaped support or “E-block” having a plurality of mutually parallel wings. The assembly of the E-block and the HGAs is called HSA and is utilized for reading or writing on one face or both the faces of one or more magnetic disks. The HSA also includes a bearing which couples the HSA to stationary component parts of the hard disk and enables the former to rotate under the control of a motor of the VCM (“Voice Coil Motor”) type, for moving the magnetic heads on the magnetic disks.
Checking operations carried out on the HSA, before the latter is assembled in the hard disk, typically include dimensional and attitude checking of the heads, of the associated sliders as well as of the E-block wings. Such checking operations are carried out by dedicated systems that typically comprise a rest structure, reference and locking devices of the HSA to be checked for referring and locking the HSA in the rest structure, checking devices for checking the conformity of the dimensions and the attitude (“roll” angle and “pitch” angle) of the HSA with the project specifications, and displacement devices of the HSA for rotating and/or translating the HSA with respect to the checking devices.
European patent No. EP 1029219 B1 discloses an optoelectronic apparatus for checking position and/or form deviation of mechanical pieces, for example HSA sliders, which includes, among other things, a base, a locking and reference system for the E-block of the HSA to be checked, detection devices with an optoelectronic system for providing signals indicative of the position of the piece component parts, a processing unit for processing signals provided by the detection devices, and a rotation system enabling mutual rotations between the piece and the optoelectronic system. In the course of mutual rotations between the HSA and the optoelectronic system, signals indicative of the spatial position of the sliders are detected by means of the optoelectronic system. Once processed, said signals provide information concerning the dimension and/or the attitude of the sliders with respect to a reference plane, which is defined by the base.
The international patent application published with No. WO 2006/097445 discloses an optoelectronic apparatus which can check dimensions and attitude of mechanical pieces, in particular HSA sliders, having smaller dimensions than those checked with the apparatus illustrated in the patent No. EP 1029219 B1.
The optoelectronic apparatus disclosed in patent publication No. WO 2006/097445 includes a base, a locking and reference system for the E-block of the HSA to be checked, a translation system, and a rotation system enabling mutual translations and rotations between the piece and the optoelectronic system, in the course of which an optoelectronic device provides signals indicative of the position of the sliders of the HSA to be checked. Such an apparatus provides remarkable standards of metrological performance and can provide measures related to height and attitude of the sliders that are referred to a locating plane defined by the base.
In the apparatuses disclosed in the previously mentioned patent documents, the sliders attitude is detected in a checking condition and is influenced by the HSA E-block, since the arrangement of the parts to be checked is established by the connection of the E-block to the locking and reference system.
The attitude of the HSA sliders in a working condition, which means once the HSA has been assembled in the associated hard disk, generally differs from the attitude that has been previously checked, owing to the influence applied not only by the E-block attitude but also by the bearing attitude, which couples to a suitable seat of the hard disk and thus determines the whole attitude of the HSA in the working condition. That is, whether attitude of the sliders is checked with reference to the E-block, the working conditions of the HSA are not taken into consideration, and this can introduce errors. In other words, sliders having an attitude according to the project specifications in a checking condition, could have an attitude differing from the project specifications in a working condition, and vice-versa.